/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.beam.runners.samza.transforms;

import org.apache.beam.sdk.transforms.Combine;

/**
 * Currently Beam only supports either throw away the accumulation or keep it after firing. This
 * CombineFn allows more flexibility to update the accumulation.
 */
public abstract class UpdatingCombineFn<InputT, AccumT, OutputT>
    extends Combine.CombineFn<InputT, AccumT, OutputT> {

  /**
   * Returns an updated accumulator from the given accumulator after firing a window pane.
   *
   * <p>For efficiency, the input accumulator may be modified and returned.
   */
  public abstract AccumT updateAfterFiring(AccumT accumulator);
}
